Process for fabricating an optoelectronic device including photoluminescent pads of photoresist

ABSTRACT

The invention relates to a method for producing an optoelectronic device ( 1 ) including a matrix array of light-emitting diodes ( 4 ) and a plurality of photoluminescent pads ( 6   1   , 6   2   , 6   3  . . . ) that are each located facing at least some of said light-emitting diodes ( 4 ), including the following steps:
         forming said plurality of photoluminescent pads ( 6   1   , 6   2   , 6   3  . . . ) by photolithography from at least one photoresist ( 5   1   , 5   2   , 5   3  . . . ) containing photoluminescent particles, said photoresist having been deposited beforehand on a supporting surface ( 3; 3 ′);   forming reflective walls ( 101, 102, 103  . . . ) covering lateral flanks ( 8   1   , 8   2   , 8   3  . . . ) of said photoluminescent pads ( 6   1   , 6   2   , 6   3  . . . ) by deposition of at least one thin-layer section ( 9   1   , 9   2   , 9   3  . . . ) on the lateral flanks.

TECHNICAL FIELD

The field of the invention is that of methods for manufacturingoptoelectronic devices including light-emitting diodes associated withphotoluminescent pads. The invention is especially applicable to displayscreens or systems for projecting images.

PRIOR ART

Various optoelectronic devices exist which include a matrix array oflight-emitting diodes having an emission surface, this emission surfacebeing at least partially coated with photoluminescent pads. Suchoptoelectronic devices may form display screens or image-projectingsystems including a matrix array of luminous pixels of various colours.

The light-emitting diodes may be based on a semiconductor comprisingelements from column III and column V of the periodic table (such as aIII-V compound) and especially gallium nitride (GaN), indium galliumnitride (InGaN) or aluminium gallium nitride (AlGaN). They are arrangedso as to form a matrix array of light-emitting diodes having an emissionsurface through which the light radiation emitted by the light-emittingdiodes is transmitted.

In the case of a display screen or an image-projecting system, theoptoelectronic device may thus include a matrix array of luminouspixels, each luminous pixels including one or more light-emittingdiodes. With the aim of obtaining luminous pixels suitable for emittinglight of various colours, for example blue, green or red, thelight-emitting diodes may be designed to emit blue light, and certainluminous pixels may include photoluminescent pads suitable for at leastpartially absorbing the blue light emitted by the light-emitting diodesand emitting, in response, green or red light. The photoluminescent padsare conventionally formed from a binding matrix including particles of aphotoluminescent material such as cerium-doped yttrium aluminium garnet(YAG:Ce).

Generally, there is a need to provide a method for manufacturing anoptoelectronic device allowing resolution to be increased whileoptimising contrast.

SUMMARY OF THE INVENTION

The aim of the invention is to provide a method for manufacturing anoptoelectronic device including light-emitting diodes andphotoluminescent pads, said method allowing high-resolution andhigh-contrast optoelectronic devices to be obtained.

To this end, one subject of the invention is a method for manufacturingan optoelectronic device for producing an optoelectronic deviceincluding a matrix array of light-emitting diodes and a plurality ofphotoluminescent pads that are each located facing at least some of saidlight-emitting diodes, including the following steps:

-   -   forming said plurality of photoluminescent pads by        photolithography from at least one photoresist containing        photoluminescent particles, said photoresist having been        deposited beforehand on a supporting surface;    -   forming reflective walls covering lateral flanks of said        photoluminescent pads by deposition of at least one thin-layer        section on the lateral flanks.

The following are certain preferred but nonlimiting aspects of thismethod.

The step of forming the reflective walls may include conformallydepositing at least one thin layer made of a reflective material so asto cover the photoluminescent pads, then locally etching the depositedthin layer so as to free what is referred to as an upper surface of thephotoluminescent pads, said upper surface being located opposite saidsupporting surface.

The steps of forming the plurality of photoluminescent pads and offorming the reflective walls may include the following steps:

-   -   forming a plurality of first photoluminescent pads by        photolithography from a first photoresist containing first        photoluminescent particles, said first photoresist having been        deposited beforehand on said supporting surface;    -   forming first reflective walls covering lateral flanks of said        first photoluminescent pads by conformally depositing a thin        reflective layer on the first photoluminescent pads and then        etching locally so as to free an upper surface of the first        photoluminescent pads; and    -   forming a plurality of second photoluminescent pads by        photolithography from a second photoresist containing second        photoluminescent particles, said second photoresist having been        deposited beforehand on said supporting surface, the second        photoluminescent particles being different from the first        photoluminescent particles.

The method may include, following the step of forming the plurality ofsecond photoluminescent pads, the step of:

-   -   forming second reflective walls covering lateral flanks of said        second photoluminescent pads by conformally depositing a thin        reflective layer on the first and second photoluminescent pads,        then etching locally so as to free the upper surface of the        first and second photoluminescent pads.

Each second photoluminescent pad makes preferably contact with at leastone first reflective wall.

Each first reflective wall has preferably a thickness comprised betweento nm and 500 nm.

The step of forming the plurality of photoluminescent pads may includeat least a step of forming a plurality of first photoluminescent padscontaining first photoluminescent particles and then forming a pluralityof second photoluminescent pads containing second photoluminescentparticles that are different from the first photoluminescent particles,the step of forming the reflective walls being carried out after atleast the first and second photoluminescent pads have been formed.

The reflective walls are preferably formed by electrodeposition.

The average size of the photoluminescent particles is preferably 500 nmor less.

The photoluminescent particles are preferably quantum dots and have anaverage size of 50 nm or less.

The photoluminescent pads have preferably an average height of 30 μm orless.

The light-emitting diodes may be elongate three-dimensional componentsextending longitudinally substantially orthogonally to a main plane of asupporting layer.

The light-emitting diodes may be located inside the photoresist pads, atleast some of which pads are photoluminescent pads includingphotoluminescent particles.

The photoluminescent pads preferably rest on a supporting surface thatis what is referred to as a transmission surface, said supportingsurface being formed by a spacer layer covering the light-emittingdiodes.

Another subject of the invention is an optoelectronic device, including:

-   -   a matrix array of light-emitting diodes resting on a supporting        layer;    -   a plurality of first photoluminescent pads that are each located        facing at least some of said light-emitting diodes and that are        each formed from a first photoresist including first        photoluminescent particles, said first photoluminescent pads        having lateral flanks covered by a deposited thin-layer section        forming a first reflective wall;    -   a plurality of second photoluminescent pads that are each        located facing at least some of said light-emitting diodes and        that are each formed from a second photoresist including second        photoluminescent particles that are different from the first        photoluminescent particles, said pads having lateral flanks        covered by a deposited thin-layer section forming a second        reflective wall.

Each second photoluminescent pad makes preferably contact with a firstreflective wall.

The light-emitting diodes have preferably a three-dimensional structurethat is elongate along a longitudinal axis that is substantiallyorthogonal to the supporting layer.

The light-emitting diodes are preferably located inside thephotoluminescent pads.

The light-emitting diodes have preferably a mesa structure.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, aims, advantages and features of the invention willbecome more clearly apparent on reading the following detaileddescription of preferred embodiments thereof, which description is givenby way of nonlimiting example and with reference to the appendeddrawings, in which:

FIGS. 1A to 1F are partial schematic cross-sectional views of varioussteps of a manufacturing method according to a first embodiment, inwhich the photoluminescent pads are produced by photolithography fromvarious photoresists containing photoluminescent particles;

FIGS. 2A to 2H are partial schematic cross-sectional views of varioussteps of a manufacturing method according to a second embodiment, inwhich the resolution of the pixels may be increased with respect to thatobtained using the method according to the first embodiment;

FIG. 3A is a schematic and partial view from above of one variant of themanufacturing method according to the second embodiment, in which thelateral flanks of each second photoluminescent pad make contact withfirst reflective walls (here it is an example of a Bayer matrix); andFIG. 3B is a schematic partial cross-sectional view of an optoelectronicdevice obtained using another variant of the manufacturing methodaccording to the second embodiment, in which the reflective walls areinclined;

FIG. 4A is a schematic partial cross-sectional view of an optoelectronicdevice obtained by the manufacturing method according to the secondembodiment, in which the light-emitting diodes are wire light-emittingdiodes, FIG. 4B illustrates in detail an exemplary wire light-emittingdiode with a core/shell configuration, and FIG. 4C illustrates anotherexemplary wire light-emitting diode with an axial configuration;

FIG. 5 is a schematic partial cross-sectional view of an optoelectronicdevice obtained by the manufacturing method according to the secondembodiment, in which the light-emitting diodes are mesa diodes;

FIGS. 6A to 6I are schematic partial cross-sectional views of varioussteps of a manufacturing method according to a third embodiment, inwhich the light-emitting diodes are located inside the photoresist pads;and

FIG. 7 is a schematic partial cross-sectional view of an optoelectronicdevice obtained by one variant of the method according to the secondembodiment, in which the reflective walls of two adjacentphotoluminescent pads make contact with each other.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

In the figures and in the rest of the description, components that areidentical or similar are referenced by the same references. In addition,the various components are not shown to scale to make the figuresclearer. Moreover, the various embodiments and variants are notexclusive of one another and may be combined together. Unless otherwiseindicated, the terms “substantially”, “about” and “of the order of” meanto within 10%.

The invention relates to a method for manufacturing an optoelectronicdevice including light-emitting diodes and photoluminescent pads. Moreprecisely, the optoelectronic device includes a matrix array oflight-emitting diodes that are distributed in various luminous pixels,the photoluminescent pads each being located facing at least some of thelight-emitting diodes. By located facing, what is meant is that thephotoluminescent pads are located directly opposite the light-emittingdiodes and may be spaced apart from or make contact with the latter.

According to one embodiment, details of which are given below, thephotoluminescent pads may be located facing the light-emitting diodesand be spaced apart from the latter by a spacer layer. In other words,the photoluminescent pads do not make contact with the light-emittingdiodes. They may rest on a supporting surface that is what is referredto as an optical transmission surface of the spacer layer. Thetransmission surface is that surface of the spacer layer through whichthe light radiation that is what is referred to as excitation radiation,emitted by the light-emitting diodes in the direction of thephotoluminescent pads, is transmitted. As a variant, the transmissionsurface may be a surface of a transparent plate on which thephotoluminescent pads have been produced beforehand, the transparentplate then being added and fastened to the matrix array oflight-emitting diodes, for example on the spacer layer.

According to another embodiment, details of which are given below, thephotoluminescent pads may be located facing the light-emitting diodesand making contact with the latter. In other words, in a luminous pixel,the light-emitting diodes are located inside and making contact with thecorresponding photoluminescent pad. The photoluminescent pad thensurrounds each of the corresponding light-emitting diodes. Thelight-emitting diodes and the photoluminescent pads rest on one and thesame supporting surface of what is referred to as a supporting layer.This embodiment is more particularly of relevance to wire light-emittingdiodes.

The photoluminescent pads are suitable for at least partially convertingthe excitation light radiation emitted by the light-emitting diodes intowhat is called luminescent light radiation of a different wavelength.Each photoluminescent pad includes a binding matrix that is transparentto the excitation and luminescent light radiation and in whichphotoluminescent particles are dispersed. The photoluminescent pads reston a supporting surface, for example a surface of a supporting layer onwhich the light-emitting diodes also rest, or a surface of a transparentspacer layer that covers the light-emitting diodes, or even a surface ofan added transparent plate. Each photoluminescent pad has, opposite thesupporting surface, what is called an upper surface that is intended totransmit the luminescent light radiation, and lateral flanks that extendfrom the upper surface as far as the supporting surface and thus boundthe pad laterally.

The binding matrix of the photoluminescent pads is here a photoresist.By photoresist, what is meant here is a material the solubility of whichin a developer changes under the effect of given light radiation that isapplied thereto, here in the context of a photolithography step. It maybe chosen from positive or negative resists, these categories ofphotoresist being known to those skilled in the art. Eachphotoluminescent pad is formed from a photoresist, which may beidentical or different from one pad to the next, including thephotoluminescent particles.

The photoresist is transparent and optically inert to the lightradiation emitted by the light-emitting diodes and by thephotoluminescent particles. Thus, the resist transmits at least 50% andpreferably at least 80% of the light emitted by the light-emittingdiodes and of the light emitted by the photoluminescent particles, andit does not emit light in response to an absorption of this light. Itmay be chosen from silicone, a polysiloxane such as polydimethylsiloxane(PDMS), the resist SU-8, thermoplastic polymers such as polymethylmethacrylate (PMMA), polyimide or from other suitable photoresists.

The photoluminescent particles are particles of at least onephotoluminescent material suitable for at least partially converting theexcitation light into luminescent light of longer wavelength. By way ofexample, they may be suitable for absorbing blue light, i.e. light thewavelength of which is comprised between about 440 nm and 490 nm, andfor emitting in the green, i.e. at a wavelength comprised between about495 nm and 560 nm, or even in the red, i.e. at a wavelength comprisedbetween 600 nm and 650 nm. By wavelength, what is meant here is thewavelength of the intensity peak of the emission spectrum. By way ofpurely illustrative example, the light-emitting diodes may have anemission spectrum the intensity peak of which is located between 380 nmand 490 nm.

The photoluminescent particles are separated from one another and may beof any shape, for example spherical, angular, applanate, elongate or ofany other shape. The size of a particle is here the smallest dimensionof the particle, and the average size is the arithmetic mean of thesizes of the particles. The photoluminescent particles may have anaverage size comprised between 0.2 nm and 1000 nm, for example lowerthan 500 nm, for example lower than 100 nm, and preferably lower than 50nm.

Preferably, the photoluminescent particles take the form of quantumdots, i.e. the form of semiconductor nanocrystals the quantumconfinement of which is substantially three-dimensional. The averagesize of the quantum dots may then be comprised between 0.2 nm and 50 nmand for example between 1 nm and 30 nm. The quantum dots may be formedfrom at least one semiconductor compound, which may be chosen fromcadmium selenide (CdSe), indium phosphide (InP), indium galliumphosphide (InGaP), cadmium sulphide (CdS), zinc sulphide (ZnS), cadmiumoxide (CdO) or zinc oxide (ZnO), cadmium zinc selenide (CdZnSe), zincselenide (ZnSe) for example doped with copper or manganese, graphene orfrom other suitable semiconductors. The quantum dots may also have acore/shell structure, the core/shell being made of material combinationssuch as CdSe/ZnS, CdSe/CdS, CdSe/CdS/ZnS, PbSe/PbS, CdTe/CdSe,CdSe/ZnTe, InP/ZnS, etc. The size and/or the composition of thephotoluminescent particles are/is chosen depending on the wavelengthdesired for the luminescence.

The photoluminescent pads each take the form of a block of photoresist,the thickness of which is defined as being its largest dimension alongan axis orthogonal to the surface on which it rests. The cross sectionof the pads, in a plane parallel to said surface on which they rest, maybe various shapes and for example circular, oval, polygonal and forexample triangular, square, rectangular or even hexagonal. Here, thewidth of a pad is defined as being a transverse dimension of a crosssection of the pad. The local width is the width of the pad at a givenheight thereof. The average width is the mean (for example thearithmetic mean) of the local widths over the thickness of the pad.

The thickness of a photoluminescent pad may be comprised between 0.1 μmand 50 μm, is preferably comprised between 1 μm and 30 μm and is forexample equal to about 20 μm. The width of a photoluminescent paddepends on that of a luminous pixel and therefore on the application ofthe optoelectronic device. It may be comprised between 0.5 μm and 1 μm,for example comprised between 1 μm and 20 μm and for example equal toabout 1 μm in the case of a display screen or a projecting system.Moreover, the fraction per unit weight of photoluminescent particles inthe photoresist may be comprised between 10% and 70%, is preferablycomprised between 25% and 60% and is for example equal to 30%. It isadapted especially depending on the thickness of the photoluminescentpad so as to allow all of the thickness of the photoresist to be exposedin a photolithography step, and on the desired light conversionefficiency.

FIGS. 1A to 1F illustrate a method for manufacturing an optoelectronicdevice including light-emitting diodes according to a first embodiment.

A direct three-dimensional coordinate system (X,Y,Z) in which the plane(X,Y) is substantially parallel to the main plane of an optoelectronicchip 2, and in which the Z-axis is oriented in a direction orthogonal tothe XY-plane, is defined here and will be referred to in the rest of thedescription.

FIG. 1A illustrates the provision of a matrix array of light-emittingdiodes having a transmission surface 3 and the deposition of a firstphotoresist 5 ₁ including first photoluminescent particles.

The matrix array of light-emitting diodes (not shown) is here formed inan optoelectronic chip 2 and defines a matrix array of luminous pixelsP. One surface of the optoelectronic chip 2 forms the transmissionsurface 3 of the matrix array of light-emitting diodes. The transmissionsurface 3 is here substantially planar, though microstructures allowinglight extraction to be improved may optionally be present therein.

The light-emitting diodes are here based on one and the samesemiconductor compound, for example a III-V compound such as GaN. Bybased on, what is meant is that the light-emitting diodes are mainlymade of said semiconductor compound. As detailed below, eachlight-emitting diode includes a stack of a first and a second dopedsemiconductor section, between which sections an active region islocated. The active region is the region of a light-emitting diode inwhich light radiation is generated. The light-emitting diodes may havevarious structures, such as wire or mesa structures, examples of whichare described below with reference to FIGS. 4B and 4C, and to FIG. 5,respectively.

In this example, the light-emitting diodes are designed to emit bluelight, i.e. light the emission spectrum of which has an intensity peakat a wavelength comprised between about 440 nm and 490 nm.

A first photoresist 5 ₁ is deposited on the light-emitting diodes, herewithout making contact with the latter. More precisely, it is depositedon a supporting surface, here the transmission surface 3 of theoptoelectronic chip 2, so as to be located facing the light-emittingdiodes. The first photoresist 5 ₁ includes first photoluminescentparticles, here quantum dots, that are suitable for at least partiallyconverting the blue light emitted by the light-emitting diodes into redlight, green light or light of another colour and here, for example, redlight. The photoresist 5 ₁ may be deposited so as to completely coverthe transmission surface 3. It may be deposited using a conventionaltechnique known to those skilled in the art, for example spin coating,spray coating, rotogravure printing, screen printing, etc.

The photoresist 5 ₁ has a substantially constant local thicknesseverywhere on the transmission surface 3, and has an average thicknessthat is preferably comprised between 0.1 μm and 50 μm, preferablycomprised between 1 μm and 40 μm and for example equal to about 20 μm.

In this example, it includes photoluminescent particles, here quantumdots, that are suitable for at least partially converting the blue lightemitted by the light-emitting diodes into red light. By way of example,quantum dots formed from CdSe semiconductor nanocrystals the averagesize of which is comprised between about 3 nm and 12 nm are suitable forconverting blue light into red light. The first photoresist 5 ₁ containsa fraction per unit weight of quantum dots that may be comprised between10% and 70%, that is preferably comprised between 25% and 60% and thatis for example equal to about 30%.

FIG. 1B illustrates a step of forming first photoluminescent pads 6 ₁ byphotolithography from the first photoresist 5 ₁. The first pads 6 ₁ areseparated from one another and are positioned on the transmissionsurface 3 of pixels P_(R) intended to emit red light.

In this example, all the first photoluminescent pads 6 ₁ havesubstantially identical dimensions to one another. They are here formedfrom a block of first photoresist 5 ₁ having a substantially square orrectangular cross section in the XY-plane. Each first photoluminescentpad 6 ₁ thus has what is called an upper surface 7 ₁ opposite thetransmission surface 3, and lateral flanks 8, that extend from the uppersurface 7 ₁ as far as the transmission surface 3. In other words, thelight-emitting diodes rest on a supporting layer (not shown) of theoptoelectronic chip, and the upper surface of the photoluminescent padsis that surface of the pads which is opposite the supporting layer alongthe Z-axis. The thickness of the first pads 6 ₁ is here substantiallyequal to 20 μm and their average width is substantially equal to thesize of a pixel, which here is for example equal to about to 10 μm.

FIG. 1C illustrates a step of depositing a second photoresist 5 ₂ on thetransmission surface 3. This photoresist may be deposited using one ofthe aforementioned techniques, so as to cover the transmission surface 3not coated with the first photoluminescent pads 6 ₁. It thus makescontact with the lateral flanks 8 ₁ of the first photoluminescent pads 6₁. In this example, it has a thickness substantially equal to that ofthe first photoluminescent pads 6 ₁ but may have a different thickness,for example a larger thickness.

In this example, the second photoresist 5 ₂ includes secondphotoluminescent particles, here quantum dots, that are suitable for atleast partially converting the blue light emitted by the light-emittingdiodes into light different from that emitted by the firstphotoluminescent particles and here, for example, green light. By way ofexample, quantum dots formed from CdSe semiconductor nanocrystals theaverage size of which is equal to about 1.3 nm are suitable forconverting blue light into green light. The second photoresist 5 ₂ maycontain a fraction per unit weight of quantum dots that is identical ordifferent from that of the first photoresist 5 ₁. Although the secondphotoluminescent particles are different from the first photoluminescentparticles, the binding matrix forming the second photoresist 5 ₂ may beidentical to that forming the first photoresist 5 ₁.

FIG. 1D illustrates a step of forming second photoluminescent pads 6 ₂by photolithography from the second photoresist 5 ₂. The second pads 6 ₂are separated from one another and are also separate from the first pads6 ₁ insofar as they do not make contact with one another. They arepositioned on the transmission surface 3 of pixels P_(G) intended toemit green light.

The second photoluminescent pads 6 ₂ may have dimensions that areidentical or different from one second pad 6 ₂ to the next, and that areidentical or different from those of the first pads 6 ₁. In thisexample, all the various pads 6 ₁, 6 ₂ have substantially identicaldimensions to one another. The second photoluminescent pads 6 ₂ are thusformed from a block of second photoresist 5 ₂ having a substantiallysquare or rectangular cross section in the XY-plane. Similar to thefirst pads, each second photoluminescent pad 6 ₂ has what is called anupper surface 7 ₂ opposite the transmission surface 3, and lateralflanks 8 ₂ that extend from the upper surface 7 ₂ as far as thetransmission surface 3.

The minimal distance, in the XY-plane, separating each photoluminescentpad 6 ₁, 6 ₂ from the neighbouring pads 6 ₁, 6 ₂ is adapted to allowreflective walls 10 ₁, 10 ₂ to be formed covering the lateral flanks 8₁, 8 ₂ of the photoluminescent pads 6 ₁, 6 ₂. This distance may thus beof the order of a few hundred nanometres to a few microns or indeedmore.

In this example, the transmission surface 3 includes zones that are notcoated with photoluminescent pads 6 ₁, 6 ₂, which zones are locatedfacing one or more light-emitting diodes, thus defining luminous pixelsP_(B) intended to emit blue light. These pixels P_(B) may have a sizesubstantially equal to those of the luminous pixels P_(G), P_(R)including photoluminescent pads 6 ₁, 6 ₂. As a variant, the zonesintended to form blue pixels may include photoluminescent pads thephotoluminescent particles of which are suitable for emitting blue lightof wavelength different from that of the blue light emitted by thediodes.

By way of example, the diodes may emit at a wavelength of about 450 nmand the photoluminescent particles may emit at a wavelength of about 480nm.

FIG. 1E illustrates a step of conformally depositing a thin layer 9 madeof at least one reflective material and for example of at least onemetal. The thin layer 9 may thus be deposited by chemical vapourdeposition (by atomic layer deposition for example) or even by physicalvapour deposition (by electron-beam physical vapour deposition orcathode sputtering for example), etc. By conformal deposition, what ismeant is that the thin layer is deposited on the photoluminescent pads 6in such a way that it extends locally substantially parallel to thesurface that it covers. The conformally deposited thin layer has asubstantially uniform thickness. Its local thickness may however varybetween a minimum value, for example at a surface that is substantiallyorthogonal to the XY-plane, and a maximum value, for example at asurface substantially parallel to the XY-plane. By way of purelyillustrative example, for a thin layer conformally deposited with athickness of 200 nm, the thickness of the layer may vary between a valueof 100 nm on the lateral flanks 8 of the pads 6 and a value of 200 nm onthe transmission surface 3 and the upper surfaces 7 of the pads 6.

The thin layer 9 may be formed from just one reflective material or froma plurality of various materials deposited on one another. Thereflective materials may be chosen from aluminium, silver, platinum orany other suitable material. The thin layer 9 has a substantiallyuniform average thickness, which may be comprised between to nm and 500nm and preferably between 50 nm and 300 nm and which is for exampleequal to about too nm on the lateral flanks 8 of the pads 6.

The thin layer 9 covers the various photoluminescent pads 6 ₁, 6 ₂ andthe transmission surface 3 not coated with the pads 6 ₁, 6 ₂. Thus, itcontinuously covers the lateral flanks 8 ₁, 8 ₂ and the upper surfaces 7₁, 7 ₂ of the first and second photoluminescent pads 6 ₁, 6 ₂, and thetransmission surface 3 located between two adjacent luminous pixelsincluding photoluminescent blocks, i.e. here the green pixels P_(G) andred pixels P_(R), and at the luminous pixels that do not include aphotoluminescent pad, i.e. here the blue pixels P_(B).

FIG. 1F illustrates a step of forming reflective walls 10 ₁, 10 ₂covering the lateral flanks 8 ₁, 8 ₂ of the photoluminescent pads 6 ₁, 6₂ by etching the thin layer 9 locally.

Thus, those portions of the thin reflective layer 9 that are not locatedin contact with the lateral flanks 8 ₁, 8 ₂ of the photoluminescent pads6 ₁, 6 ₂ are etched. Thus, the portions of the thin layer 9 that coverthe upper surfaces 7 ₁, 7 ₂ of the photoluminescent pads 6 ₁, 6 ₂ areremoved, and the portions of the thin layer 9 that cover the zones ofthe transmission surface 3 defining the blue pixels P_(B) are alsoremoved. Thus, the upper surfaces 7 ₁, 7 ₂ and the transmission surface3 covered by the thin layer 9 are freed. By free, what is meant is thatthe surfaces are not covered by a layer. Those portions of the thinlayer 9 which are located on the transmission surface 3 between twoadjacent luminous pixels P_(G), P_(R) including photoluminescent blocksare also removed. Thus, the lateral flanks 8 of the pads 6 are coveredby the reflective walls 10. In other words, the reflective walls to reston the lateral flanks and continually cover them while making contacttherewith.

This etching step may be a step of dry etching and for example a step ofplasma etching (RIE, ICP, etc.). Since dry etching is highlyanisotropic, only the portions of the thin reflective layer 9 coveringthe lateral flanks 8 ₁, 8 ₂ of the photoluminescent pads 6 ₁, 6 ₂remain, thus forming reflective walls 10 ₁, 10 ₂ that encircle thephotoluminescent pads 6 ₁, 6 ₂ in a plane parallel to the XY-plane.

The layer of the transmission surface 3 may act as an etch stop for thedry etching of the metal, thus allowing the integrity of thelight-emitting diodes to be preserved. It may thus be a face of aplanarisation layer made of an organic or mineral material, or even apassivation layer made of a dielectric material, for example siliconoxide (for example SiO₂), silicon nitride (for example Si₃N₄), orsilicon oxynitride (SiON).

Thus, the manufacturing method according to this first embodiment allowsan optoelectronic device having a high resolution and a high contrast tobe obtained. Specifically, using a photoresist containingphotoluminescent particles and advantageously quantum dots, it ispossible to form the photoluminescent pads directly by photolithography.Thus, it is possible to obtain a matrix array of photoluminescent padsof high resolution, while avoiding recourse to alternative techniquessuch as localised deposition of droplets containing photoluminescentparticles. Such techniques have drawbacks especially related to thecontrol of the size of the droplets, the alignment of thedroplet-dispensing head with respect to the luminous pixels, etc. whichmay prevent the desired resolution from being obtained. In addition, theformation of reflective walls by conformal deposition then local etchingallows a high contrast to be obtained insofar as the light radiationassociated with a pixel cannot reach the photoluminescent block of aneighbouring pixel.

FIGS. 2A to 2H illustrate a method for manufacturing an optoelectronicdevice 1 comprising light-emitting diodes according to a secondembodiment.

FIG. 2A illustrates a step of providing a matrix array of light-emittingdiodes and a step of depositing of a first photoresist 5 ₁ includingfirst photoluminescent particles. The steps are identical or similar tothose described with reference to FIG. iA and are not described ingreater detail.

FIG. 2B illustrates a step of forming first photoluminescent pads 6 ₁ byphotolithography from the first photoresist 5 ₁. This step is alsosimilar or identical to that described with reference to FIG. 1B.

FIG. 2C illustrates a step of conformally depositing a first thin layer9 ₁ made of at least one reflective material. In contrast to the firstembodiment, the first thin reflective layer 9, is deposited before thesecond photoluminescent pads 6 ₂ have been formed.

The first thin layer 9, may thus be deposited by one of theaforementioned techniques. It may be formed from one and only onereflective material or from a plurality of various materials depositedon one another, and have a substantially constant thickness, for exampleequal to about 100 nm.

It covers the first photoluminescent pads 6 ₁ and the transmissionsurface 3 not coated with the first pads 6 ₁. Thus, it continuouslycovers the lateral flanks 8 ₁ and the upper surface 7 ₁ of the firstphotoluminescent pads 6 ₁, and those zones of the transmission surface 3which are intended to form the other luminous pixels, i.e. here thegreen pixels P_(G) and blue pixels P_(B).

FIG. 2D illustrates a step of forming, by local etching of the firstthin layer 9 ₁, the first reflective walls 10 ₁ covering the lateralflanks 8 ₁ of the first photoluminescent pads 6 ₁.

Thus, those portions of the thin layer 9 ₁ that are not located incontact with the lateral flanks 8, of the first photoluminescent pads 6₁ are etched. Thus, the portions of the thin layer 9 that cover theupper surfaces 7 ₁ of the first photoluminescent pads 6 ₁ are removed,and the portions that cover the zones of the transmission surface 3defining the green pixels P_(G) and blue pixels P_(B) are also removed.

This etching step may be a step of dry etching and for example a step inwhich one of the aforementioned techniques is implemented. Since dryetching is highly anisotropic, only the portions of the first thin layer9 ₁ covering the lateral flanks 8 ₁ of the first photoluminescent pads 6₁ remain, thus forming the first reflective walls 10 ₁ that encircle thefirst photoluminescent pads 6 ₁, in a plane parallel to the XY-plane.

FIG. 2E illustrates a step of depositing a second photoresist 5 ₂ on thetransmission surface 3. It may be deposited using one of theaforementioned techniques so as to cover the transmission surface 3 notcoated with the first photoluminescent pads 6 ₁. It thus makes contactwith the reflective walls 10 ₁ of the first pads 6 ₁, and, in thisexample, has a thickness that is substantially equal to that of thefirst photoluminescent pads 6 ₁. The second photoresist 5 ₂ includessecond photoluminescent particles, here quantum dots, that are similaror identical to those described in the first embodiment.

FIG. 2F illustrates a step of forming second photoluminescent pads 6 ₂by photolithography from the second photoresist 5 ₂. In this example,they are positioned on the transmission surface 3 of pixels P_(G)intended to emit green light.

In contrast to the first embodiment, at least one secondphotoluminescent pad 6 ₂, and here each second photoluminescent pad 6 ₂,is located against a first photoluminescent pad 6 ₁ so as to makecontact with the corresponding first reflective wall 10 ₁. Here said padmakes contact with at least one first reflective wall 10, but alsoincludes at least one free lateral-flank portion 8 ₂, i.e. a portionthat does not make contact with a first reflective wall 10 ₁.

The second photoluminescent pads 6 ₂ are separated from one another andare also separated from the first photoluminescent pads 6 ₁. Each secondpad 6 ₂ is moreover optically and structurally separated from the firstpad 6 ₁ against which it is located by the first reflective wall 10 ₁.Thus, the luminescent light radiation emitted by the firstphotoluminescent particles cannot be transmitted to the adjacent secondphotoluminescent pad 6 ₂, nor that of the second photoluminescentparticles transmitted to the adjacent first photoluminescent pad 6 ₁.

FIG. 2G illustrates a step of depositing a second thin layer 9 ₂ made ofa reflective material. The second thin layer 9 ₂ may be formed from oneor more materials that are identical to that or those of the first thinlayer 9 ₁. Preferably, the second thin layer 9 ₂ is identical, in termsof material and thickness, to the first thin layer 9 ₁.

The second thin layer 9 ₂ is deposited so as to cover the first andsecond photoluminescent pads 6 ₁, 6 ₂ and the transmission surface 3 notcoated with the photoluminescent pads 6 ₁, 6 ₂. Thus, it continuouslycovers the upper surfaces 7 ₁, 7 ₂ of the first and secondphotoluminescent pads 6 ₁, 6 ₂, the lateral flanks 8 ₂ of the secondphotoluminescent pads 6 ₂, and the first reflective wall 10 ₁ of thefirst photoluminescent pads 6 ₁. It also covers those zones of thetransmission surface 3 which are intended to form the blue pixels P_(B).

FIG. 2H illustrates a step of forming, by local etching of the secondthin layer 9 ₂, second reflective walls 10 ₂ covering the lateral flanks8 ₂ of the second photoluminescent pads 6 ₂ that do not make contactwith a first reflective wall 10 ₁. Thus, those portions of the secondthin layer 9 ₂ that are not located in contact with the lateral flanks 8₂ of the second photoluminescent pads 6 ₂ are etched. Thus, the portionsof the thin layer 9 ₂ that cover the upper surfaces 7 ₁, 7 ₂ of thefirst and second photoluminescent pads 6 ₁, 6 ₂ are removed, and theportions that cover the zones of the transmission surface 3 defining theblue pixels P_(B) are also removed.

This etching step may be a step of dry etching and for example a step inwhich one of the aforementioned techniques is implemented. Since dryetching is highly anisotropic, only the portions of the second thinlayer 9 ₂ covering the lateral flanks 8 ₂ of the second photoluminescentpads 6 ₂ remain, thus forming second reflective walls 10 ₁. Whereas eachfirst reflective wall 10, continuously encircles, in a plane parallel tothe XY-plane, the corresponding first photoluminescent pad 6 ₁, eachsecond reflective wall 10 ₂ makes contact only with one portion of thelateral flanks 8 ₂ of the corresponding second photoluminescent pad 6 ₂.It may clearly be seen that one portion of the first reflective wall 10,is covered by one portion of the second reflective wall 10 ₂, thisresulting in an increased local thickness of reflective material.

Thus, the method according to the second embodiment allows anoptoelectronic device having an even higher resolution to be obtained,insofar as the first and second photoluminescent pads 6 ₁, 6 ₂ locatednext to each other are mutually separated only by a single reflectivewall the thickness of which may be smaller than 500 nm and for exampleabout equal to 100 nm or indeed less. It is thus possible to increasethe resolution of the optoelectronic device, while maintaining a highcontrast between the pixels.

According to one variant illustrated in FIG. 3A, the luminous pixels arearranged so as to form a Bayer matrix, i.e. so as to form a geometricrepetition of a set of a plurality of luminous pixels suitable foremitting at different wavelengths, for example two green pixels P_(G),one red pixel P_(R) and one blue pixel P_(B), which pixels are arrangedadjacently pairwise.

In this example, a given green pixel P_(G) is adjacent to four differentred pixels P_(R). More precisely, a given second photoluminescent pad 6₂ suitable for converting blue excitation light into green light, isbordered by four first photoluminescent pads 6 ₁ that are separated fromone another and suitable for converting the blue excitation light intored light. Each second pad 6 ₂ thus makes contact with the firstreflective walls 10 ₁ of four adjacent first pads 6 ₁.

Thus, this variant of the method according to the second embodiment doesnot include a step of forming second reflective walls 10 ₂ covering thelateral flanks 8 ₂ of the second pads 6 ₂. Specifically, during thedeposition of the second photoresist 5 ₂, the latter fills the spacesformed between the first photoluminescent pads 6 ₁ and more preciselythe spaces formed between the mutually facing first reflective walls 10₁. The second photoresist 5 ₂ is then removed by photolithography fromthe zones intended to form blue luminous pixels P_(B). The secondphotoluminescent pads 6 ₂ thus formed therefore make contact with thereflective walls 10 ₁ of a plurality of neighbouring firstphotoluminescent pads 6 ₁. They are therefore bounded laterally, in theXY-plane, by the first reflective walls 10 ₁.

Other arrangements of the luminous pixels are of course possible. Thus,in the example in FIG. 3B, along the X-axis, the first photoluminescentpads 6 ₁ are spaced apart pairwise either by a second photoluminescentpad 6 ₂ or by a zone of the transmission surface 3 that is intended toform a blue pixel P_(B).

According to another variant illustrated in FIG. 3B, the reflectivewalls 1 o, are inclined with respect to the XY-plane. By inclined, whatis meant is that the reflective walls 1 o, have an angle of inclinationother than 90⁰ to the XY-plane. This angle of inclination may thus bestrictly smaller than 90⁰ and larger than or equal to a maximum nonzerovalue of inclination that, for example, may be equal to about 20°. Thesewalls are here substantially planar and have a substantially constantlocal angle of inclination. The first photoluminescent pads 6 ₁, whichare preferably suitable for converting the excitation light into thered, have a truncated pyramidal shape, i.e. the area occupied by theupper surface 7 ₁ is smaller than that occupied by the base of the padmaking contact with the transmission surface 3.

In contrast, the second photoluminescent pads 6 ₂, which are preferablysuitable for converting the excitation light into the green, have aflared shape, insofar as the area occupied by the upper surface 7 ₂ islarger than that occupied by the base. They thus have an invertedtruncated pyramidal shape. The fact that the second photoluminescentpads 6 ₂ have a shape that is flared outwards allows the extraction ofthe luminescent light radiation to be improved. Specifically,reabsorption of the luminescent radiation by the same photoluminescentparticles can thus be limited, this being particularly advantageous whenthe latter are suitable for emitting luminescent light in the green.

As a variant, the reflective walls 10 ₁, 10 ₂ need not be planar, butmay have a curved shape, in particular when the first photoluminescentpads 6 ₁ have substantially curved lateral flanks 8 ₁. By curved, whatis in particular meant is a surface that is devoid of planar zones, orthat is formed from a succession of planar zones that are inclinedpairwise. It is then possible to limit the partial etching of thereflective walls 10 ₁, 10 ₂ in the step of dry etching of the thinreflective layers 9 ₁, 9 ₂ while optimising the extraction of light andwhile limiting the reabsorption of the luminescent light of the secondphotoluminescent pads 6 ₂.

Generally, the light-emitting diodes may have various types ofstructures. FIGS. 4A and 4B illustrate an example of wire-typelight-emitting diodes 4, here in the configuration called the core-shellconfiguration.

With reference to FIG. 4A, the optoelectronic device includes anoptoelectronic chip 2 in which the matrix array of light-emitting diodes4 is located. Each luminous pixel thus includes a plurality of wirelight-emitting diodes 4. The light-emitting diodes 4 may be uniformlydistributed in each luminous pixel, and form sets of diodes that areelectrically separate from one another. Thus, each set of diodes belongsto one luminous pixel, which may be activated independently of the othersets of diodes. In a given set, the light-emitting diodes 4 areconnected in parallel, so as to emit simultaneously when thecorresponding pixel is activated.

The light-emitting diodes 4 rest on a supporting layer 25, for example agrowth substrate. In the case where the growth substrate 25 iselectrically insulating, electrical lines (not shown) may be present inthe interior of the substrate 25 in order to allow the various pixels oflight-emitting diodes 4 to be biased. In the case of an electricallyconductive growth substrate 25, for example one based on silicon, trenchisolations (not shown) may be provided to electrically isolate thepixels from one another. Moreover, the supporting layer 25 may befastened and electrically connected to a control chip (not shown)suitable for ensuring the electrical control of the optoelectronicdevice.

The light-emitting diodes 4 are coated with at least one spacer layer 12the face of which opposite the supporting layer forms the transmissionsurface 3. The spacer layer 12 is transparent to the light radiationemitted by the light-emitting diodes 4. It may be formed by apassivation layer produced from a dielectric material, and optionallyfrom a planarisation layer. The dielectric material may be chosen froman oxide, a nitride or even a silicon oxynitride. Other materials mayalso be suitable. The planarisation layer may be formed from an organicor mineral material such as silicone or PMMA. The spacer layer has athickness larger than the longitudinal dimension, along the Z-axis, ofthe light-emitting diodes 4, so as to cover them uniformly.

FIG. 4A illustrates an exemplary light-emitting diode 4 belonging to agiven luminous pixel, which diode is a wire diode in a core/shellconfiguration. The light-emitting diode 4 has an elongatethree-dimensional shape and extends longitudinally along an axisparallel to the Z-axis. In this example, it includes a first dopedsection 21, which, for example, is n-doped, taking the form of a wirethat extends longitudinally from a nucleation pad 24 that rests on afront side of a growth substrate 25. A growth mask 26 made of adielectric material covers the front side of the substrate 25 andincludes an aperture opening onto the nucleation pad 24. The nucleationpads 24 may be pads that are separated from one another, or even variouszones of a given thin continuous layer. An upper portion of the firstdoped section 21 is covered, at its upper border and its lateral border,by one or more layers forming an active zone 23 that includes at leastone quantum well. The active zone 23 is itself covered by a layerforming a second doped section 22 that here is p-doped. Thelight-emitting diodes 4 are here nanowires or microwires in a core/shellconfiguration, the doped section 21 and the doped section 22 forming thecore and the shell of the wire, respectively.

The light-emitting diodes 4 of a given luminous pixel are hereelectrically connected in parallel. The back side of the substrate 25,which here is electrically conductive, is coated with a first biasingelectrode 27, and the doped sections 22 are covered with a continuouslayer forming a second biasing electrode 28. Lastly, the spacer layer 12entirely covers the light-emitting diodes 4. Said layer has a heresubstantially planar upper face that forms the transmission surface 3 ofthe matrix array of light-emitting diodes 4.

FIG. 4C illustrates another exemplary light-emitting diode 4 belongingto a given luminous pixel, which diode is a wire diode in an axialconfiguration. In this example, the wire is formed by a stack of thefirst doped section 21, of the active zone 23 and of the second dopedsection 22, which extends along a longitudinal axis parallel to theZ-axis. In contrast to the core/shell configuration, the active zone 23covers substantially only the upper border of the doped section 21, andthe doped section 22 covers substantially only the upper border of theactive zone 23. As above, the wire extends longitudinally from anucleation pad 24 that rests on a front side of a growth substrate 25.The growth mask 26 covers the front side of the substrate 25 andincludes an aperture opening onto the nucleation pad 24. The spacerlayer covers the lateral border of the wire, and is passed through bythe second biasing electrode 28 that makes contact with the upper borderof the second doped section 22. The spacer layer 12 has an upper facethat forms the transmission surface 3.

Purely by way of illustration, the light-emitting diodes 4 may be basedon GaN and be suitable for emitting excitation radiation in the blue.They may have transverse dimensions comprised between 10 nm and 10 μmand for example comprised between 100 nm and 5 μm. Their height islarger than their transverse dimensions and for example 2 times, 5times, and preferably at least 10 times larger, and may be equal toabout 10 μm.

FIG. 5 illustrates an optoelectronic device in which the light-emittingdiodes 4 have a mesa structure. In this example, each luminous pixelincludes a single light-emitting diode 4 that may be activatedindependently of the other diodes 4.

The light-emitting diodes 4 are each formed by a stack of a first dopedsection 31, here of n type, and of a second doped section 32, here of ptype, between which sections an active zone 33 is located. They formmesa structures that are substantially coplanar with one another. Thisstructure of the light-emitting diodes 4 is similar or identical to thatdescribed in document EP2960940, the text of which is considered to beintegrally incorporated into the present description. By mesa structure,what is meant is a structure formed from a stack of semiconductorsections 31, 32, 33 that protrude above a growth substrate following anetching step. The mesa structures are substantially coplanar in so faras the first doped sections 31 of the light-emitting diodes 4 arerespectively coplanar. The same goes for the active zones 33 and thesecond doped sections 32.

Each light-emitting diode 4 has a first doped section 31 a surface ofwhich opposite the active zone 33 is a surface via which the lightradiation of the diode 4 is emitted. The lateral flanks of the firstdoped section 31 and of the second doped section 32, and those of theactive zone 33, are covered with a dielectric layer 34, except for at abreakout surface 35 of the first doped section 31.

The light-emitting diodes 4 are separated from one another by lateralelectrical connection components 36 that extend along the Z-axis betweenthe diodes. Each light-emitting diode 4 is thus associated with alateral connection component 36 that makes electrical contact with thebreakout surface 35 of the first doped section 31, allowing a determinedelectrical potential to be applied to the first doped section 31. Thislateral connection component 36 is however electrically insulated fromthe adjacent diodes 4 by the dielectric layers 34 thereof.

The optoelectronic chip 2 in this example includes a layer 37 called anelectrically connecting layer that forms a supporting layer, the layer37 allowing electrical contact between the control chip (not shown) andi) the lateral electrical connection components 36, and ii) electricalconnection sections 38 located in contact with the second doped sections32. The connecting layer 37 thus includes connection pads 39 that areelectrically insulated from one another by a dielectric material. Thus,the control chip may apply an electrical potential to any one of thelight-emitting diodes 4, and thus activate them independently of oneanother.

The spacer layer 12 here includes a passivation layer made of adielectric material covering the lateral connection components 36 andthe emission face of the first doped sections 31 of the light-emittingdiodes 4, said spacer layer optionally being completed with aplanarisation layer. The face of the spacer layer 12 that is oppositethe light-emitting diodes 4 forms the transmission surface 3 of thediode matrix array.

Purely by way of illustration, the light-emitting diodes 4 may be basedon GaN and be suitable for emitting light radiation in the blue. Theymay have a thickness comprised between too nm and 50 μm, and theirlateral dimensions may be comprised between 500 nm and a few hundredmicrons, and preferably are smaller than 50 μm, preferably smaller than30 μm, and may be equal to 10 μm or even 5 μm.

As a variant to the first and second embodiments, in which embodimentsthe photoluminescent pads 6 are produced directly on an emission surface3 of a matrix array of light-emitting diodes, the steps of forming thephotoluminescent pads 6 and the reflective walls 10 may be carried outon what is referred to as a supporting surface of a plate that istransparent to the light radiation emitted by the light-emitting diodes,the transparent plate then being added and fastened to the matrix arrayof light-emitting diodes and for example to the spacer layer. The methodaccording to this variant is then similar to those of the first andsecond embodiments described above, the emission surface 3 then being asurface of the transparent plate. The transparent plate may be producedfrom glass and especially a borosilicate glass such as Pyrex, or fromsapphire, or from any other suitable material. It has a thicknesspermitting it to be handled and therefore added to the diodes. Thetransparent plate may be fastened to the matrix array of light-emittingdiodes and for example to the aforementioned spacer layer by any means,for example by adhesive bonding using an adhesive that is transparent tothe light radiation emitted by the diodes. After the step of adding thetransparent plate to the matrix array of light-emitting diodes, thephotoluminescent pads are each located facing at least onelight-emitting diode.

FIGS. 6A to 6I illustrate a method for manufacturing an optoelectronicdevice 1 comprising light-emitting diodes according to a thirdembodiment, which embodiment differs from the first and secondembodiments essentially in that the diodes are wire diodes and locatedinside photoresist pads, certain or all of which are photoluminescent.By located inside, what is meant is that the photoresist pad encircleseach of the corresponding light-emitting diodes in the XY-plane andcovers them along the Z-axis. The light-emitting diodes therefore makecontact with the photoresist of the pad and are not spaced aparttherefrom by the spacer layer as in the first and second embodiments.

FIG. 6A illustrates a step of providing a matrix array of wirelight-emitting diodes that preferably have a core/shell configuration.The light-emitting diodes 4 here have a structure that is identical orsimilar to that shown in FIG. 4B, with the exception of the spacer layer12. They thus take the form of an elongate three-dimensional structurethat extends along a longitudinal axis parallel to the Z-axis from thesurface of a supporting layer, for example the growth substrate 25.

The light-emitting diodes 4 are arranged on the supporting layer 25 insets of light-emitting diodes, which sets are intended to form luminouspixels of various emission colours, for example here blue pixels P_(B),red pixels P_(R) and green pixels P_(G). Thus, preferably, the diodes ofa given set, and therefore of a given luminous pixel, are electricallyconnected in parallel, and each set of diodes is electricallyindependent of the other sets. By way of illustration, thelight-emitting diodes 4 may have a height equal to about 10 μm. In thisexample, they are based on GaN and are suitable for emitting blueexcitation light.

FIG. 6B illustrates a step of depositing on a supporting surface 3′,here the surface of the supporting layer 25, a first photoresist 5 ₁including first photoluminescent particles. The photoresist 5 ₁ makescontact with and covers the surface 3′ of the supporting layer 25, andmakes contact with and covers each light-emitting diode 4 on itsemission surface. It thus extends, in a plane parallel to the XY-plane,between each of the light-emitting diodes 4, and has a thickness largerthan the height of the light-emitting diodes 4. By way of illustration,the first photoresist 5 ₁ may have a thickness equal to about 20 μm. Thefirst photoluminescent particles may here be suitable for convertinginto red light the blue excitation light emitted by the light-emittingdiodes 4. They are here quantum dots, the average size of which issmaller than 50 nm.

FIG. 6C illustrates a step of forming first photoluminescent pads 6 ₁ byphotolithography from the first photoresist 5 ₁. The firstphotoluminescent pads 6 ₁ are localised inside the zones intended toform red luminous pixels P_(R). Thus, each first pad 6 ₁ covers andextends between the light-emitting diodes 4 of the corresponding pixelP_(R). In other words, the diodes 4 of the pixels P_(R) are locatedinside the first pads 6 ₁, and are not located a distance away therefromas in the first and second embodiments described above.

By way of illustration, the first pads 6 ₁ have a thicknesssubstantially equal to 20 μm and a width substantially equal to 10 μm.The first photoluminescent pads 6 ₁ have a width such that each firstpad 6 ₁ extends on the corresponding luminous pixel P_(R), and does notextend over the zones intended to form the neighbouring luminous pixelsP_(B) and P_(G) of other colours. The zones intended to form luminouspixels of other colours, for example here the blue pixels P_(B) andgreen pixels P_(G), do not include first photoluminescent pads 6 ₁.

FIG. 6D illustrates a step of depositing a second photoresist 5 ₂including second photoluminescent particles. The latter are differentfrom the first photoluminescent particles insofar as their emissionspectrum is different from that of the first photoluminescent particles.In this example, they are suitable for converting into green light theblue excitation light emitted by the light-emitting diodes 4. They arehere quantum dots, the average size of which is smaller than 50 nm. Thesecond resist 5 ₂ makes contact with and covers the surface 3′ of thesupporting layer 25, and makes contact with and covers eachlight-emitting diode 4 not located in the first pads 6 ₁. It thusextends, in a plane parallel to the XY-plane, between the light-emittingdiodes 4 located inside the zones intended to form the blue luminouspixels P_(B) and the green luminous pixels P_(G), and has a thicknesslarger than the height of the light-emitting diodes 4. By way ofillustration, the second photoresist 5 ₂ may have a thicknesssubstantially equal to about 20 μm.

FIG. 6E illustrates a step of forming second photoluminescent pads 6 ₂by photolithography from the second photoresist 5 ₂. The second pads 6 ₂are localised in the zones intended to form green luminous pixels P_(G).Each second pad 6 ₂ thus covers the light-emitting diodes 4 of thecorresponding pixel P_(G), and extends between the diodes 4 while makingcontact therewith. In other words, the diodes 4 of the pixels P_(G) arelocated inside the second pads 6 ₂. By way of illustration, the secondpads 6 ₂ have a thickness substantially equal to 20 μm and a widthsubstantially equal to 10 μm. The second pads 6 ₂ have a width such thateach second pad 6 ₂ extends in the corresponding luminous pixel P_(G),and does not extend over the zones intended to form the neighbouringblue luminous pixels P_(B). The zones intended to form blue luminouspixels P_(B) do not include second photoluminescent pads 6 ₂.

FIG. 6F illustrates a step of depositing a third photoresist 5 ₃ so thatit covers the diodes located in zones intended to form blue pixelsP_(B). It makes contact with and covers the surface 3′ of the supportinglayer 25. The third photoresist 5 ₃ may or may not include thirdphotoluminescent particles that are different from the first and secondphotoluminescent particles. In the case where it does not includephotoluminescent particles, the luminous pixel P_(B) is suitable foremitting light the spectrum of which corresponds to that of thelight-emitting diodes. In this example, it includes thirdphotoluminescent particles, here quantum dots the average size of whichis smaller than 50 nm, suitable for converting the blue excitation lightemitted by the light-emitting diodes 4 into blue light of anotherwavelength. By way of example, the diodes may emit at a wavelength ofabout 450 nm and the third particles may be suitable for emittingluminescent light at about 480 nm. The third resist 5 ₃ makes contactwith and covers the surface of the supporting layer, and makes contactwith and covers each diode 4 not located in the first and second pads 6₁ and 6 ₂. It thus extends, in a plane parallel to the XY-plane, betweenthe light-emitting diodes 4 located in the zones intended to form blueluminous pixels P_(B), and has a thickness larger than the height of thelight-emitting diodes 4. By way of illustration, the third photoresist 5₃ may have a thickness substantially equal to about 20 μm.

FIG. 6G illustrates a step of forming third pads 6 ₃, herephotoluminescent pads, by photolithography from the third photoresist 5₃. The third pads 6 ₃ are localised in zones intended to form blueluminous pixels P_(B). Each third pad 6 ₃ covers and extends between thediodes 4 of the corresponding pixel P_(B), while making contacttherewith. In other words, the diodes 4 of the pixels P_(B) are locatedinside the third pads 6 ₃. By way of illustration, the third pads 6 ₃have a thickness substantially equal to 20 μm and a width substantiallyequal to 10 μm. The third pads 6 ₃ have a width such that each third pad6 ₃ extends in the corresponding blue luminous pixel P_(B).

FIG. 6H illustrates a step of conformally depositing a thin layer 9 madeof at least one reflective material and for example at least one metal,so as to cover the first, second and third pads 6 ₁, 6 ₂, 6 ₃. The thinlayer thus continuously coats the upper surfaces 7 ₁, 7 ₂, 7 ₃ and thelateral flanks 8 ₁, 8 ₂, 8 ₃ of the pads 6 ₁, 6 ₂, 6 ₃. It may have asubstantially uniform thickness, for example, equal to about 100 nm, onthe lateral flanks 8 of the pads 6.

FIG. 6I illustrates a step of forming reflective walls 10 ₁, 10 ₂, 10 ₃covering the lateral flanks 8 ₁, 8 ₂, 8 ₃ by locally etching the thinlayer 9. Thus, the portions of the thin layer 9 that cover the uppersurfaces 7 ₁, 7 ₂, 7 ₃ are etched, here by dry etching. The portions ofthe thin layer 9 that rest on the surface 3′ of the supporting layer 25are also etched.

Thus, with the manufacturing method according to the third embodiment,it is possible to obtain an optoelectronic device the wire-typelight-emitting diodes of which are located inside the photoresist pads,at least some of which are photoluminescent. A high resolution may beobtained because the photoresist pads are produced by photolithographyand because the photoluminescent particles are quantum dots.

FIG. 7 illustrates a variant of the method according to the thirdembodiment in which the thin reflective layer 9 is deposited so that itsthickness on the lateral flanks 8 ₁, 8 ₂, 8 ₃ of the pads 6 ₁, 6 ₂, 6 ₃is larger than half the distance that separates two neighbouring pads inthe XY-plane. Thus, in the step of depositing the thin layer 9, acontact is obtained between the mutually facing reflective walls to oftwo neighbouring pads 6.

As a variant of FIG. 7 and of the third embodiment described above, thereflective walls 10 may be formed by electrodeposition. More precisely,as illustrated in FIGS. 6A-6G, photoresist pads 6 are produced that reston a surface 3′ of the supporting layer 25. A thin growth track,produced from at least one metal, for example from titanium, copper oraluminium, is located on the surface 3′ of the supporting layer 25, andextends between pairwise neighbouring pads 6, so as to encircle each ofthe pads 6. Next, as a variant to FIGS. 6H and 6I, the reflective wallsto are produced by electrodeposition of a reflective material, such as ametal, for example nickel, aluminium or silver. The metal then growsfrom the thin growth layer, and fills the space bounded by the mutuallyfacing lateral flanks 8. The metal thus covers the lateral flanks of thepads 6 and forms the reflective walls. The optoelectronic device 1 isthen similar to that illustrated in FIG. 7 in the sense that thereflective walls to fill the space formed between neighbouring pads 6.By way of illustration, the distance between two neighbouring pads 6 maybe comprised between 0.5 m and 5 m.

As a variant to the method according to the third embodiment describedabove, the first, second and third photoluminescent pads 6, and thecorresponding reflective walls to may be produced successively. Moreprecisely, similarly to the second embodiment, the firstphotoluminescent pads 6 ₁ are formed, then the first reflective walls 10₁ are formed, then the second photoluminescent pads 6 ₂ are formed, thenthe second reflective walls 10 ₂ are formed, and so on.

Particular embodiments have just been described. Various variants andmodifications will seem obvious to those skilled in the art. Thus, thelight-emitting diodes may be suitable for emitting excitation light in acolour other than the blue, and the various photoluminescent pads may besuitable for converting the excitation light into colours other than thered and the green. Furthermore, the pads may not contain anyphotoluminescent particles. Moreover, generally, the photoluminescentpad 6 may have thicknesswise and/or widthwise dimensions that aredifferent from one another.

1-17. (canceled)
 18. A method for producing an optoelectronic device,wherein said optoelectronic device includes a matrix array oflight-emitting diodes and photoluminescent pads, each of which faces atleast some of said light-emitting diodes, said method comprising formingsaid photoluminescent pads by photolithography from at least onephotoresist that contains photoluminescent particles, said photoresisthaving been deposited beforehand on a supporting surface and formingreflective walls covering lateral flanks of said photoluminescent padsby deposition of at least one thin-layer section on said lateral flanks.19. The method of claim 18, wherein forming said reflective wallscomprises conformally depositing at least one thin layer made of areflective material so as to cover said photoluminescent pads and, afterhaving done so, locally etching said deposited thin layer so as to freean upper surface of said photoluminescent pads, said upper surface beinglocated opposite said supporting surface.
 20. The method of claim 19,wherein said forming said photoluminescent pads and forming saidreflective walls includes forming first photoluminescent pads byphotolithography from a first photoresist containing firstphotoluminescent particles, said first photoresist having been depositedbeforehand on said supporting surface, forming first reflective wallscovering lateral flanks of said first photoluminescent pads byconformally depositing a thin reflective layer on said firstphotoluminescent pads and then etching locally so as to free an uppersurface of said first photoluminescent pads, forming secondphotoluminescent pads by photolithography from a second photoresistcontaining second photoluminescent particles, said second photoresisthaving been deposited beforehand on said supporting surface, said secondphotoluminescent particles differing from said first photoluminescentparticles.
 21. The method of claim 20, further comprising, followingforming said second photoluminescent pads, forming second reflectivewalls covering lateral flanks of said second photoluminescent pads byconformally depositing a thin reflective layer on said first and secondphotoluminescent pads and then etching locally so as to free said uppersurface of said first and second photoluminescent pads.
 22. The methodof claim 20, wherein each second photoluminescent pad contacts at leastone first reflective wall.
 23. The method of claim 19, wherein eachfirst reflective wall has a thickness that is between ten nanometers andfive hundred nanometers.
 24. The method of claim 18, wherein formingsaid photoluminescent pads includes forming first photoluminescent padscontaining first photoluminescent particles and forming secondphotoluminescent pads containing second photoluminescent particles thatare different from said first photoluminescent particles, whereinforming said reflective walls comprises forming said reflective wallsafter at least said first and second photoluminescent pads have beenformed.
 25. The method of claim 24, wherein forming said reflectivewalls comprises forming said reflective walls by electrodeposition. 26.The method of claim 18, wherein said photoluminescent particles arequantum dots that have an average size that is no greater than fiftynanometers.
 27. The method of claim 18, wherein said light-emittingdiodes are elongate three-dimensional components that extendlongitudinally substantially orthogonally to a main plane of asupporting layer.
 28. The method of claim 27, wherein saidlight-emitting diodes are located inside said photoresist pads andwherein at least some of said photoresist pads are photoluminescent padsthat include photoluminescent particles.
 29. The method of claim 18,wherein said photoluminescent pads rest on a supporting surface, whereinsaid supporting surface is a transmission surface, and wherein a spacerlayer that covers said light-emitting diodes forms said supportingsurface being formed by a spacer layer covering said light-emittingdiodes.
 30. An apparatus comprising an optoelectronic device, saidoptoelectronic device comprising a matrix array of light-emitting diodesresting on a supporting layer, first photoluminescent pads, and secondphotoluminescent pads, wherein each of said first photoluminescent padsis located facing at least some of said light-emitting diodes, whereineach of said first photoluminescent pads is formed from a firstphotoresist that includes first photoluminescent particles, wherein eachof said first photoluminescent pads comprises lateral flanks covered bya deposited thin-layer section forming a first reflective wall, whereineach of said second photoluminescent pads faces at least some of saidlight-emitting diodes, wherein second photoluminescent pads is formedfrom a second photoresist that includes second photoluminescentparticles, wherein said second photoluminescent particles differ fromsaid first photoluminescent particles, and wherein said secondphotoluminescent pads comprise lateral flanks that are covered by adeposited thin-layer section that forms a second reflective wall. 31.The apparatus of claim 30, wherein each of said second photoluminescentpads contacts said first reflective wall.
 32. The apparatus of claim 30,wherein said light-emitting diodes have a three-dimensional structurethat is elongated along a longitudinal axis that is orthogonal to saidsupporting layer.
 33. The apparatus of claim 32, wherein saidlight-emitting diodes are located inside said first or secondphotoluminescent pads.
 34. The apparatus of claim 31, wherein saidlight-emitting diodes have a mesa structure.